The art of power tools and/or machines provides many different makes and models of power driven drill presses, lathes, saws, mills and the like for performing work on various materials. The prime movers in a large percentage of such machines are constant speed electric motors and the motors are drivingly connected with power driven shafts of the related machines by pulley and belt drive means which enable the operators of the machines to adjust the speed at which the input shafts of the machines are driven. The pulley and belt drive means typically include pairs of multi-diameter/multi-sheave pulley wheels on the motor driven shafts and driven shafts and belts engaged with and about the pulleys, whereby the driven shafts can be made to operate or to rotate at one of the limited number of predetermined operating speeds afforded by the pulley and belt drive means. If the pulley wheels of the belt and pulley drive means are three or four sheave wheels, three or four operating speeds are afforded thereby and the range of speeds is necessarily and/or generally quite limited. For example, a typical motor which operates at 1,750 RPM driving the driven shaft of a related machine through and/or by means of a three sheave multi-diameter pulley and belt drive means is capable of driving the input shaft at for example, 875 RPM, 1,750 RPM and 3,450 RPM, by shifting or moving the belt of the drive means into engagement with related pairs of sheaves of the pulley wheels.
The work that most power driven machines can perform is limited, to a great extent, by the speed at which the machines can be operated. Thus, the use to which a machine having a limited range of operating speeds can be put is limited. As a general rule, if the range of operating speeds of a machine can be increased, the uses to which that machine can be put is also increased.
Common characteristics in power driven machines of the general character referred to above resides in the fact that an excess of ninety percent of such machines are equipped and driven by NATIONAL ELECTRICAL MANUFACTURERS ASSOCIATION NO. 56 FRAME MOTORS, hereinafter referred to and/or identified as N.E.M.A. #56 Frame Motors, or Standard Motors. N.E.M.A. #56 Frame Motors are dimensionally similar and are characterized by like shaft diameter, like shaft length, like keyways, like mounting plates or frames having like fastener receiving openings. Further, the machines with which such motors are related are characteristically provided with motor mounting pads with motor mounting studs projecting therefrom or with fastener receiving openings which are complimentary with the mounting frames of the motors, to facilitate easy, convenient and accurate mounting of the motors.
In the art of power driven machines of the general character referred to above and which are here concerned with, there has been a long existing want and need for a means whereby the operating speeds of the machines can be easily, conveniently and effectively substantially decreased and substantially increased so as to extend the useful purposes to which the machines can be put.